Parthenium hysterophorus L. - a predominant weed flora among phytosociology of Islamabad, Pakistan.

Parthenium hysterophorus belonging to family Asteraceae is a fast maturing invasive weed native to the subtropics of North and South America and now a cumbersome weed in Pakistan. Its invasion in Pakistan is of recent era and spreading like wild fire. Hence documentation of its infestation in various areas of the country is immensely important. A survey was conducted in five randomly selected residential sectors of Islamabad Pakistan selected randomly viz. F-8, G-8, I-10, G-9 and H-9. The data were recorded on absolute density, relative density, frequency and relative frequency. The data reveal the highest relative density percentage (23.41%, 11.36%, 19.11%, 30.65%, and 28.88%) for top ranking weed. Cynodon dactylon was recorded for at sectors F-8, G-8, I-10, G-9 and H-9 respectively. Parthenium emerged as the next predominant species across the various Sectors. The data exhibit that it even surpassed the C. dactylon at I-10 (20.42%) and H-9 (15.55). While the minimum relative density (7.29 %) of Parthenium occurred in sector G-9 along the roadsides Mean data across all 5 locations further exhibit that C. dactylon was the predominant Species with relative density of 22.68% followed by Parthenium (13.42%) and A. viridis (10.33%). C. sativa prevailed at a mean density of only 7.9%. It is speculated that C. sativa; one of the predominant natives species in the past has been replaced with Parthenium at many a locations studied. The dominance of C. sativa followed by Parthenium, across all sectors was depicted. However, the highest relative frequency (66.84%) of C. sativa was recorded in Sector I-10. The computation of Importance value further exhibit that Cynodon-Parthenium-Euphorbia community dominated at F-8. While at G-8, PartheniumEuphorbia-Cynodon was prevalent. In I-10. CannabisParthenium-Boerhavia community dominated, whereas at G-9 Boerhavia-Cynodon-Cannabis Parthenium-Cannabis community was evidenced, looking at the overall distribution of flora in Islamabad Capital Territory the Cynodon-Parthenium-Cannabis